The Alias alum put on a pair of swimming goggles and sat behind a fairground-style cardboard cutout to play Fallon's take on the classic game which has the same rules as Rock, Paper, Scissors, but involves the loser getting pied in the face at the end.
At first it looked like Fallon would be the one facing the plate of pie, as he lost two rounds in a row against Ben Affleck's wife's. But when he turned the handles on his pie machine, the former SNL comedian was in luck, because his sticky missile didn't launch.
As Danny Collins star Garner lost her first round to Fallon, it looked like she was going to get away pie free too — but the actress had a sixth sense about her second shot at the pie machine, and sure enough, a white, fluffy cream pie was delivered splat into her face.
Laughing at his guest's misfortune, Fallon reminded Garner she had plans after the show.
"Yeah I'm going to a Broadway play!" she replied.
"You're going to smell like milk," the show host added.
Watch the video above and see what happened when Garner took a second pie to the face!